1. Field of the Invention
This invention relates to the field of image scanners, and more specifically to the field of motion picture digitizer interfaces.
2. Background Art
Film scanners have been developed to digitize films for storage and processing in a digital form. Storing motion picture images in a digital form has many advantages over storing motion picture images using film. These advantages include the fact that digital images can be readily duplicated with no loss of image quality, digital images can be readily enhanced by computers, digital films can be stored indefinitely, and digital films can be distributed electronically.
Typically a digital film scanner digitizes a film frame using a light source which exposes a film frame and projects an image. The projected image passes through a lens and onto a sensor. The sensor then converts the image into data for storage. Generally a film frame image is exposed by several colored light sources. For example, an image may be first exposed by a red light source, then a green light source, then a blue light source. Some digital film scanners use a sensor as large or larger than the projected image. Other digital film scanners use a sensor smaller than the projected image.
A line-array sensor is a sensor having a width smaller than the width of projected film frame images. This requires the projected images to be moved across the line-array sensor to expose the entire projected image to the sensor. One way to scan a film frame using a line-array sensor is to move a lens so as to move the projected image across the sensor. The height of the projected image at the sensor is smaller than or equal to the height of the sensor. Therefore, to expose the line-array sensor to the entire projected image requires only that the projected image move perpendicular to the line-array sensor. The lens moves along an axis parallel to the plane of the film gate, and perpendicular to the direction of film transport. Moving the lens in this manner moves the projected image across the vertical face of the sensor, and thereby exposes the sensor to the entire projected image, one line at a time. This type of scanning sub-system is described in more detail in the co-pending application "METHOD AND APPARATUS FOR SCANNING AN IMAGE USING A MOVING LENS SYSTEM," David DiFrancesco, Ser. No. 08/664,266, filed Jun. 11, 1996, and assigned to the assignee of this application.
A variety of motion generating means may be used to move the lens in a moving lens scanner. For example, a cam connected to the lens via a spring mounted base can be used to move the lens. In one type of cam driven scanner a motor rotates the cam, causing the lens to make a full cycle of movement with each complete rotation of the cam. The horizontal scanning movement of the lens allows the sensor to only have to cover the generally shorter vertical axis of the film frame. The lens may expose the sensor to a full frame in each direction of its motion. Scanning images during both directions of the lens movement maximizes efficiency by avoiding having the sensor wait for the lens to return. Alternatively, an image may be scanned as the lens moves in one direction only, with a wait period following each scan for the lens to return to the start position. The scanning speed is generally limited by the speed of the sensor. To obtain full resolution from a sensor requires that the sensor be exposed to a threshold number of photons.
An alternative to using a moving lens is to use a moving mirror system to scan projected images across the sensor, as is known by those of ordinary skill in the art. An example of a scanner that uses a moving mirror system to scan projected images across a sensor is described in U.S. Pat. No. 4,330,793, entitled "ELECTRONIC SCANNING OF SUPER-8 FILMS FOR REPRODUCTION ON A T.V. VIEWING UNIT," the disclosure of which is hereby incorporated by reference. The tilting mirror system is very similar to that used in galvanometric systems, although slight structural modifications may be necessary with regard to the magnetic system thereof. Such systems provide the precise controllability of deflection required by the scanner.
Image scanner references include:
In U.S. Pat. No. 5,249,056 Foung et al. describe an apparatus for generating video signals from a photographic image previously recorded on film (a cine video system) which includes a film transport mechanism, an image projector, a video pickup system which receives the image and generates a video signal which represents it, and an output circuit which produces a resultant output video signal. The system performs rudimentary image processing techniques including black and white contrast enhancement. The system may process the data as the data is read out of frame memory. The system may then display this data on a video monitor at a rate of up to 30 film frames per second.
In U.S. Pat. No. 4,205,337 Millward describes an apparatus for producing motion picture film by scanning the film horizontally at a scanning station while transporting the film continuously past the scanning station with means for accommodating different film sizes, transport speeds, and film format by changing the frequency of the horizontal scan while performing a predetermined number of horizontal line scans in respect of each frame of the film, The line scan signals are stored in a memory, and the memory is read to produce a plurality of television picture fields at a different frequency from that at which scanning takes place. The frequency at which the television picture fields are generated is higher than that at which the line scan is effected so that the two are made temporally compatible by repeating certain television fields in order to "fill-in" for spare time.
In U.S. Pat. No. 4,729,015 Wagensonner describes a system for making positive copies from diapositives. Diapositives are copied on negative photosensitive paper in an apparatus wherein the positive is electronically scanned, line-by-line, and the density signals thereby obtained are electronically inverted prior to influencing the beam of a CRT or laser which is used to reproduce the image of the positive on paper, either line-by-line or point-by-point. The inversion of signals renders it possible to scan the high-transmissivity portions of the positives with a narrow beam, i.e., with a high degree of resolution.
Typically, motion picture film digitizers digitize a series of film frames, store that data on a magnetic tape or a collection of hard drives, and then later perform image processing operations. Digital signal processing operations that often must be performed by motion picture film digitizers include: filtering, color correction, minification, and magnification. This two step process is used because the interface between the projected image sensor and the processor is too slow to perform the required image processing of the high resolution color images as they are digitized. Thus, a higher speed interface and image processor are needed to perform the complex image processing required for high resolution color motion picture film digitization.